Pickling is widely used in hot-rolled sheet metal blank that the removal of surface oxide scale, such as hot-rolled steel pipe in need of phosphate or other surface coating before processing to remove iron oxide; welded pipes in galvanized or other hot-dip galvanizing, plating surface preparation prior to processing; steel annealing treatment, such as surface treatment of pipes, profiles, wire and other drawing before processing; plated steel machined parts, electrical rust treatment before plating and stainless steel and special steel production process similar treatment. Currently pickling steel production still is an integral part of the steel surface treatment processes. However, the use of steel pickling process has also brought some problems as follows:
(1) consume a lot of steel materials and acids
In the pickling process, some primarily by the chemical reaction of the acid and the metal dissolved in the dissolution of the corresponding metal oxide to remove the iron. Some, such as the use of sulfuric acid pickling of steel, but also by means of acid and steel peeling action of a chemical reaction to produce hydrogen bubbles to remove oxide scale. Therefore, in the pickling process, the large consumption of acid is inevitable. Although the use of acid inhibitor can reduce the metal in the pickling of steel consumption, but there is still a considerable amount of metallic iron lost.
(2) degrade the physical properties of steel
In the pickling process, the chemical reaction between the metallic iron and hydrogen gas is generated and the acid. Since the chemical potential of hydrogen in the pickling solution is higher than the pickled steel chemical potential of hydrogen, the hydrogen will be generated and accumulates them into the steel causing hydrogen embrittlement, and thus affect the mechanical properties of the steel or after the processing.
(3) bring a series of environmental pollution problems
Pickling process for the surface treatment of steel or part, due to the variety of steel, the size of product specifications and production vary, resulting in the production equipment has a very different and production environment. Such aspects seal pickling tank body, the production equipment corrosion, pickling plant exhaust ventilation, mist discharge and treatment and sewage treatment and disposal, etc., treatment methods and treatment level disparities. Which will bring many environmental aspects of the problem, and needs to be addressed and resolved eleven.
(4) waste acid and iron salts
Pickling of steel in the same time consumes a large amount of metallic iron is also produced large amounts of waste acid solution of iron salt and the corresponding acid and iron oxide or generated. In order to recover and utilize these waste acid and iron salts, requires a large investment to build the appropriate recycling and processing equipment. Especially for some small, small quantities of steel parts pickling treatment, often appear difficult to focus on the case of pickling liquid waste treatment, once the case of direct discharge occurs, it will cause serious pollution to the environment.
Post time: Sep-27-2019